[Qemu-devel] [PATCH 2/2] monitor: fix object_del for command-line-created objects

[Michael Roth <mdroth@linux.vnet.ibm.com>]

Currently objects specified on the command-line are only partially
cleaned up when 'object_del' is issued in either HMP or QMP: the
object itself is fully finalized, but the QemuOpts are not removed.
This results in the following behavior:

  x86_64-softmmu/qemu-system-x86_64 -monitor stdio \
    -object memory-backend-ram,id=ram1,size=256M

  QEMU 2.7.91 monitor - type 'help' for more information
  (qemu) object_del ram1
  (qemu) object_del ram1
  object 'ram1' not found
  (qemu) object_add memory-backend-ram,id=ram1,size=256M
  Duplicate ID 'ram1' for object
  Try "help object_add" for more information

which can be an issue for use-cases like memory hotplug.

This happens on the HMP side because hmp_object_add() attempts to
create a temporary QemuOpts entry with ID 'ram1', which ends up
conflicting with the command-line-created entry, since it was never
cleaned up during the previous hmp_object_del() call.

We address this by adding a check in user_creatable_del(), which
is called by both qmp_object_del() and hmp_object_del() to handle
the actual object cleanup, to determine whether an option group entry
matching the object's ID is present and removing it if it is.

Note that qmp_object_add() never attempts to create a temporary
QemuOpts entry, so it does not encounter the duplicate ID error,
which is why this isn't generally visible in libvirt.

Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Markus Armbruster <armbru@redhat.com>
Cc: Eric Blake <eblake@redhat.com>
Cc: Daniel Berrange <berrange@redhat.com>
Cc: qemu-stable@nongnu.org
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Reviewed-by: Daniel P. Berrange <berrange@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
---
 qom/object_interfaces.c    | 9 +++++++++
 tests/check-qom-proplist.c | 4 ++--
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/qom/object_interfaces.c b/qom/object_interfaces.c
index ded4d84..994d0c7 100644
--- a/qom/object_interfaces.c
+++ b/qom/object_interfaces.c
@@ -5,6 +5,7 @@
 #include "qapi-visit.h"
 #include "qapi/qobject-output-visitor.h"
 #include "qapi/opts-visitor.h"
+#include "qemu/config-file.h"
 
 void user_creatable_complete(Object *obj, Error **errp)
 {
@@ -209,6 +210,14 @@ void user_creatable_del(const char *id, Error **errp)
         error_setg(errp, "object '%s' is in use, can not be deleted", id);
         return;
     }
+
+    /*
+     * if object was defined on the command-line, remove its corresponding
+     * option group entry
+     */
+    qemu_opts_del(qemu_opts_find(qemu_find_opts_err("object", &error_abort),
+                                 id));
+
     object_unparent(obj);
 }
 
diff --git a/tests/check-qom-proplist.c b/tests/check-qom-proplist.c
index e3f56ca..ddec574 100644
--- a/tests/check-qom-proplist.c
+++ b/tests/check-qom-proplist.c
@@ -437,9 +437,9 @@ static void test_dummy_createcmdl(void)
      * check for this in user_creatable_del() and remove the QemuOpts if
      * it is present.
      *
-     * FIXME: add an assert to verify that the QemuOpts is cleaned up
-     * once the corresponding cleanup code is added.
+     * The below check ensures this works as expected.
      */
+    g_assert_null(qemu_opts_find(&qemu_object_opts, "dev0"));
 }
 
 static void test_dummy_badenum(void)
-- 
1.9.1